Soon, a note from Donghai County was sent to Chang'an, Taiji Palace, and Li Yuanji's desk.

This note does not use the 800-mile expedited, the 800-mile expedited is too hurtful, although it can be done under the modern system, but it is not an important military situation or the like, and few people will use the 800-mile expedited.

And they used the ordinary speed of 300 miles, but even if it was only the most ordinary 300 miles, it was also the lowest speed of daily transmission of letters after the post station system was put into use, and when the letters arrived in Chang'an, the time was only less than eight days.

After reading this recital, Li Yuanji once again felt that his energy was a little insufficient.

It's so simple, such an ordinary common-sense question, I can even ignore it.

If it is just one thing, any person in later generations will know that the ship is to use paint, and this paint is divided into many kinds, first of all, the steel used in the hull should be galvanized, so as to improve the anti-rust ability of the steel itself.

Then there is the primer, the middle coat, and the outermost coat of paint, after which the bottom part of the boat is truly completed.

And these lacquers are not ordinary lacquers, but special lacquers, how these things are made, Li Yuanji doesn't know, but he knows that lacquer must be used.

And this letter is also very clear, that is, I hope that the imperial court can find a coating with high viscosity, which can make it adhere to the steel and have the ability to prevent rust, so as to achieve the purpose of anti-rust of the hull steel.

My thoughts are still wandering.

I remember that the shipbuilding industry in the history of China started relatively late, and it was also a leapfrog development.

Unlike Europe, which consisted of wooden ships to wood-clad copper, then wood-clad iron, and subsequent warships made of pure steel.

The development of hull materials, in fact, can also be regarded as the development of anti-rust treatment capabilities in history, wood-clad copper, although to a certain extent to improve the durability of the hull, but this improvement is not large, and the cost is huge.

That's why it was changed to wood-clad iron, or wood-clad steel, which naturally has a better effect, but the problem also arises, or the problem encountered before using wood-clad copper, rust.

With the passage of time, coupled with the advancement of scientific research priorities, various paints have been studied and applied to the hull, which has gradually changed the structure of the hull to pure steel, thus improving the safety of the hull by countless levels.

In later generations, these special materials such as artillery steel and ship steel have special requirements, and even in the 21st century, there are many countries that do not have production capacity, or the raw materials produced are unqualified.

If you look at it at the level of later generations, the materials produced by Datang now are not qualified, and even those materials that are unqualified in later generations are better than the best materials in Datang now.

But that's not how the account is calculated, the warships of later generations are facing missile attacks, and the attack strength of missiles can be the same as the attack strength of artillery shells?

Of course, it is different, so the requirements for steel for warships in the 21st century are naturally higher than in the mid-to-late 20th century.

During World War II, it was the era of ironclad giant ships, and the combat effectiveness of each ship was resounding, and during the First Sino-Japanese War, the two periods were different, so the battleships during World War II had higher requirements for steel than during the First Sino-Japanese War.

And before the First Sino-Japanese War, a battleship made of wood-clad steel was considered the most advanced warship, so what else is there to say?

In other words, the demand for steel for warships does not look at the ability of steel itself, but the overall environment of the whole world and the strength of the opponent.

And now, the so-called enemies of later generations are either primitive times or nest times, and no one will think of sailing to the sea, and they don't even have the ability to gather ships and send an army of 1,000 people to dozens of nautical miles away.

Therefore, even if Li Yuanji pulls out a wooden-structure sail human-powered hybrid ship now, it is still the most advanced warship in the world, and it is an existence that they will never dare to approach.

In such an environment, what are the good requirements for the quality of steel? It is to make ordinary iron, as long as it can ensure that it does not have problems, it can guarantee that it will be ahead of the world for thousands of years.

Therefore, Li Yuanji has never been worried about material problems, so he has ignored more problems.

The development of China's shipbuilding industry is somewhat special, this is a wooden ship, to a small number of, or even only a few wood-clad steel ships, and then directly to the era of pure steel warships.

did not experience the only way for the spread and development of those countries in Europe, of course, this was only because China did not have the ability to manufacture warships at that time, and the relevant technology was introduced in the later period, so a certain part was directly skipped.

But Li Yuanji seems to remember that someone on the forum in later generations once mentioned a sentence, although it sounded a little sad and a little five-cent, and at that time, Li Yuanji only glanced at it, but he didn't care.

But when he saw this letter now, he subconsciously remembered the post he saw back then.

Why hasn't China experienced the era of wood-clad iron? Because for the problem of rust prevention of steel, there is no problem at all for Huaxia, as the country of origin of lacquer trees, Huaxia is not short of these things, and raw lacquer can be used as a ship bottom paint, but the effect is not as good as them, but even so, raw lacquer can also be used.

"I seem to remember that when I was in the north of the town a few years ago, I seemed to have seen a special kind of tree somewhere, and after cutting its body, the blood that flowed out was not colorless and transparent, but white, thicker than goat's milk." Thinking of the lacquer tree, Li Yuanji thought that he seemed to have seen it in Zhenbei back then, so he immediately summoned Ma Zhou.

The reason why this incident has an impression is because there was some small movement at that time, and the soldiers felt that those trees had become essences, because there has always been a saying among the people that some trees became essences, and their blood was red, and many people had seen it, so after seeing this, they also thought that the trees had become essences.

But how could Li Yuanji believe this? Although I didn't look at it, I ordered all these trees to be cut down and looked at, and the blood that flowed from all the trees was this color, so the matter was settled.

But where have you seen it? This Li Yuanji really forgot.

"Yes! This tree is called the oil tree, and there are many of this tree around the north of the town, and it is also a treasure. When Ma Zhou heard this description, he immediately thought of that kind of tree.

"Or a treasure?" Li Yuanji was stunned, what kind of treasure is the lacquer tree? Can you eat or what? And raw lacquer is a natural paint, is it difficult to use paint on the body to prevent mosquitoes and insects? Or against the cold?

"Speaking of this, it was the old fairy who discovered it first, when the old fairy occasionally saw that kind of tree, he felt that this tree was extraordinary, so he studied it for a while, and found that its seeds can be squeezed out of oil, and if it is eaten by people, it has some benefits.

Moreover, the old fairy also found that there are few mosquitoes around this kind of tree, except for some insects on the leaves, there are no insects on the branches and near the main body.

Then I tried it one by one, and found that the white viscous blood was collected, and after drying, it could be effectively used to repel mosquitoes on the body, and then the old fairy also found that these dried blood were still a traditional Chinese medicine, saying that it could pass through menstruation, repel insects, suppress cough or something, I heard that the old fairy himself wrote the medical book has collected this flavor of medicinal materials, and also named it Youzhi. Ma Zhou explained in detail.

Li Yuanji, who is not oily, doesn't know, and he is not a traditional Chinese medicine, how can he know this?

But according to Ma Zhou's description, nine times out of ten, what he was looking for was this so-called oil tree.

And the old immortal, that is, Sun Simiao, when the queen fled to Zhenbei, the old Taoist who saved the lives of their mother and son on the way, and then settled down in Zhenbei, came to Chang'an two years ago, served as the director of medicine in Chang'an Academy, and taught student medicine.

Well, when Sun Simiao heard that the blood transfusion to Zhang Gongjin was actually useful, this old Taoist priest who had long stopped seeing a doctor and was concentrating on cultivating and teaching students couldn't help jumping out anymore, and now he is studying with those imperial doctors in the imperial hospital.

"It was ordered to prohibit the collection of tree blood, send someone to collect some of it, send some to Donghai County, let them smear it on the hull, and then dry it and then go to the sea for testing, and the other part was brought back to the Academy of Sciences directly, so that they could use public relations technology." Li Yuanji ordered directly.

He doesn't care if the raw paint is durable, no matter how durable it is, it is also paint, and it is also a pure natural paint, not to mention more, is it okay to carry it for three or five months?

Datang has no opponents now, even if the sailors who have just formed and are waiting to be redressed, they still have no opponents, they have enough time to drive these ships back to the dock for repainting and repair, and raw paint is not a problem for Datang.

With the lacquer tree of the Tang Dynasty, it is no problem to feed one hundred and ten warships, and once it is determined to be effective, it can be planted on a large scale, and when the newly planted lacquer tree grows, what are you afraid of?

Is it nothing more than to build a few more docks, or just build a special ship? The kind of platform that can be built at sea, pumped out of the seawater, and then the boat sits on the bottom and painted directly at sea without a dock?

Thinking of this, Li Yuanji shook his head, this idea is too fantastical, with Datang's current ability, it is impossible to do this at all, for them, it is more reliable to honestly study how to make the effect of lacquer stronger.

Ma Zhou didn't hesitate, this is not a big deal, the next order, but it takes a month to send raw lacquer, and it can be sent to Donghai County in a month and a half, neither labor nor money, just running errands.